Underground tubular structural system and process for producing it

A method for producing an underground tubular structural system by adding a supplementary conduit to an existing conduit, said existing conduit (S1) being formed by associated longitudinal elements which comprise in cross-section a lower element (1) resting on the ground and at least one vault-shaped upper element (2') resting along longitudinal bearing members (16) on lateral sides (14) of said lower element (1), said process comprising the steps of

• (a) opening a trench (B) containing said existing conduit until said existing conduit (S1) is completely uncovered;
• (b) removing said upper element (2') and replacing it by an intermediate element (6) having a lower face (61) comprising a central part in the shape of a plate (60) and two lateral parts (63) respectively provided with lower longitudinal bearing members (65) resting on said longitudinal bearing members (16) of said lower element (1) and said intermediate element (6) having an upper face (62) provided with two upper longitudinal bearing members (66) similar to those of said lower element (1);
• and
• (c) closing said supplementary conduit (S2) by capping said intermediate element (6) with said upper element (2') which was previously removed and which comes to rest on said bearing parts (66) of said upper face (62) of said intermediate element (6).

An underground tubular structural system comprising in cross-section at least two sections arranged in parallel relation in a single longitudinal direction and positioned on a bottom (A) of a trench (b) and covered by a fill, said system comprising at least two conduits (S1, S2) of large cross-section constituted by prefabricated elements each covering a part of said cross-section in a transverse direction, said at least two conduits, namely, a low conduit (1) and a high conduit (S2), being superposed on one another, and said structural system comprising, in cross-section, at least three elements, namely,

• (a) a lower element (1) comprising a flat bed-plate resting on the ground (A) and having two lateral sides (14) respectively provided with bearing members (16) each constituted by a groove having a concave profile;
• (b) at least one intermediate element (6) comprising a floor (62) extending horizontally and having two substantially vertical lateral parts (63) respectively provided on two opposing faces, respectively with lower (65) and upper (66) longitudinal bearing members;
• (i) said intermediate element (6) capping said lower element (1) and resting on said bearing members (16) of said two lateral sides (14) along said lower bearing members (65) for closing said low conduit (S1);
• (ii) said lower bearing members of said intermediate element (6) each comprising an elongated centering shoulder (65) projecting along said lateral side (63) of said intermediate element (6) and engaging, when said elements are superposed, in a corresponding hollow groove (16) of said lower element (1);
• (iii) said upper bearing members (66) of said intermediate element (6) each being constituted by a groove having a profile identical to the profile of said grooves (16) of said lower element (1);
• and
• (c) a vault-shaped upper element (2') having two lateral sides respectively provided with two longitudinal bearing members (33') each having a profile identical to the profile of said centering shoulders (65) of said intermediate element (6), said vault-shaped element (2') capping said intermediate element for closing said high conduit (S2) and resting along its longitudinal bearing members (33') each engaging, when said elements are superposed, in the corresponding groove (66) of said intermediate element (6).